Specific vertices shoot off in random directions when bevelling
This turned out to be an easy fix, somewhere along this line my 'surface normals' got all messed up, and Blender's vertices follow their respective surface normals when transforming like in the bevel tool.

To resolve this problem (unless you have custom surface normals and resetting isn't an option) is to simply select the area which is not behaving as expected (in this case the edge loops and recalculate normals. For Mac the shortcut for this is shift + N. 

See more about it here